Keratoconjunctivitis sicca (KCS) results from qualitative or quantitative deficiencies in the tear film that may lead to corneal deterioration and blindness. The treatment for KCS consists primarily of tear replacement therapy and hygenic care of the anterior eye. The development of an effective therapy may be advanced by a better understanding of the cellular controls of secretion by the lacrimal gland, a major source of the tear constituents. The intent of the proposed work is to investigate the mechanism of control by bioactive peptides. It is proposed that ACTH and enkephalins are two components of a system of multiple neurotransmitters and modulators of lacrimal secretion and that their actions are mediated through cAMP. The experiments suggested trace the steps in control by ACTH and enkephalins of the secretory process. These steps include extracellular signalling, transduction at the membrane via adenylate cyclase, production of the intracellular messenger cAMP and the final cellular response, secretion. Interactions of ACTH and enkephalins will be assessed at each level. Furthermore, the cellular regulation of peptide levels by degradative aminopeptidases will be studied. The biological relevance of ACTH and enkephalins to secretion will be assessed by several methods using rat lacrimal gland tissues in vitro. The levels of the peptides in the gland will be measured by radioimmunoassay (RIA). This technique is highly sensitive and allows quantitative analysis. The source of ACTH in the glands will be determined by measurement of this peptide in the plasma and gland extracts of intact and hypophysectomized animals. The physiological significance of these peptides in lacrimal function will be assessed by in vitro perifusion of gland fragments with ACTH and enkephalins and measurement of secreted peroxidase, an enzyme marker of lacrimal protein secretion. Because the effects of ACTH and enkephalins are mediated by cAMP in other tissues, adenylate cyclase activity and the accumulation of intracellular cAMP in lacrimal tissues will be measured (by RIA) in response to these peptides. Finally, a spectrophotometric assay will be used to determine the activity of aminopeptidases in the lacrimal gland. These exopeptidases are known to degrade enkephalins in ocular tissues. Because aminopeptidase activity in lacrimal gland differs between males and females, this enzyme as well as its substrate, enkephalin, will be measured in glands from both sexes.